High frequency amplifier



2 Sheets-Sheet 1 R. S. HOLMES HIGH FREQUENCY AMPLIFIER Filed June 24,1956 oo oo 1 ,2 fi -w J o 0 0 ow & o 0 0 0 1 0 0 0 March 15, 1938.

ZSnventor (Ittorneg March 15, 1938. HOLMES 2,111,397

HIGH FREQUENCY AMPLIFIER v Filed June 24, 1936 2 Sheets-Sheet 2 Mml'mnentor Gttorneu Patented Mar. 15, 1938 UNITED STATES ?ATENT OFFICEHEGH FREQUENCY AMPLIFIER of Delaware [application June 24, 1936, SerialNo. 86,906

6 Claims.

My invention relates to high frequency amp-lifiers and particularly tointermediate frequency amplifiers for short Wave receivers such astelevision receivers.

5 An object of my invention is to provide an im proved high frequencyamplifier which is stable and efficient in operation.

A further object of my invention is to provide an improved multi-stageamplifier in which the 10 unshielded signal leads are short.

In the preferred embodiment of my invention I employ amplifier units ofthe general type described and claimed in application Serial No. 76,338,filed April 25, 1936, in the name of Loy E.

15 Barton, and assigned to the Radio Corporation of America. Each ofthese units is a complete unitary amplifier stage comprising a shieldedintermediate frequency transformer and a shielded amplifier tube havingan electrode terminal at the 20 top of the tube. In accordance with thepreferred embodiment of my invention, this electrode terminal is a gridterminal and successive amplifier units. are mounted in staggeredrelationship whereby the grid terminal of the amplifier tube 25 of oneamplifier stage is positioned close to the point in the adjacentamplifier stage from which the grid lead extends. Thus the grid lead maybe short, and feed-back difficulties and the like are avoided.

30 Other objects, features, an advantages of my invention will appearfrom the following description taken in connection with the accompanyingdrawings in which Figure 1 is a View of a portion of a television 35receiver embodying my invention,

Fig. 2 is a circuit diagram of the amplifier shown in Fig. 1,

Fig. 3 is a view in perspective of a field strength receiver embodyingmy invention and i Fig. 4 is a view showing the construction of theamplifier units illustrated in Fig. 1.

Referring to Fig. 1, my invention is shown applied to an intermediatefrequency amplifier in a television receiver in which the chassis is 10-45 cated in a vertical position. The chassis frame and one leg uponwhich is supported are indicated at l and 2, respectively. Six tubesockets for a portion of the television receiver are shown on the lefthand end of the chassis frame.

50 In the particular receiver illustrated, the intermediate frequencyamplifier comprises three amplifier stages, these stages consisting ofthree units, 3, 3 and 5. Each of these units is similar to the amplifierunit described and claimed in 55 the above identified Bartonapplication. As will be more fully explained later, the amplifier unitsare mounted on the chassis frame I in staggered relation in order tomake possible the use of short grid leads.

As illustrated in Fig. 4, where the amplifier unit 5 is shown more indetail, each amplifier unit consists of an intermediate frequencytransformer 1 supported from the under-side of a vacuum tube socket 8.The transformer l is shielded by means of a threaded shielding cap 9which is at- 10 tached to the socket cl and by means of a shielding canit which is held in screw threaded relation with the shielding cap. Theamplifier tube is inserted on the upper side of the tube socket asindicated at E2. Unless it is a metal tube or the like which does notrequire shielding, a suitable shield 13 is provided for shielding thetube.

In each amplifier stage the amplifier tube is of the type which has anelectrode terminal at the top of the tube. In the embodiment of theinvention which is illustrated, this being a preferred embodiment, thiselectrode terminal is the control grid terminal of the amplifier tube.In the amplifier stage 4 it is indicated by the reference numeral it. Aswill be explained later, this terminal may be the plate terminal of thetube.

The amplifier unit 4 is provided with a resistor and condenser panel I6upon which the filter resistors ll and filter condensers is of theamplifier stage are mounted.

The grid lead for connecting the amplifier stage 1 to the succeedingamplifier stage 5 is indicated at E9. The circuit connections of thethree stage amplifier will now be described with reference to Fig. 2.

Referring to Fig. 2, the three amplifier tubes included in the threeamplifier stages 3, 4 and 6 shown in Fig. 1 are illustrated at 2i, l2and 22, respectively. Since all three amplifier stages are alike, onlyone complete amplifier stage has been shown, this being the stageincluding the amplifier tube 22. The portion of the amplifier which isshielded is enclosed by the upper dotted rectangle 23. The resistors lland condensers 18 Which are mounted on the panel ll: are enclosed by thelower dotted rectangle 24. It will be understood that, of all theelements enclosed by the upper rectangle 23, the vacuum tube 12 is theonly one which is positioned above the vacuum tube socket, the remainingelements being located underneath the socket and being shielded by thetransformer shield I I. Each amplifier stage includes filter resistorsl1 .and filtering condensers l3 for preventing high frequency signalsfrom feeding back to cause in- Ill stability of the amplifier.Additional by-pass condensers l9 and 20 are provided for the samepurpose.

The intermediate frequency transformer I is of conventional designcomprising a tuned primary 26 and a tuned secondary 21, the primarybeing shunted by a resistor 28 in order to broaden the tuning. In theparticular amplifier illustrated, each amplifier stage is provided witha trip circuit 29 which is tuned to the intermediate frequency soundsignal for the purpose of preventing it from being included in thepicture output, this receiver being designed to receive pictures andsound simultaneously cn two carrier waves having a suitable frequencyspacing.

It will be seen from the circuit diagram that the grid lead of eachamplifier stage is the connection from the high voltage end of thetransformer secondary to the control grid of the succeeding amplifiertube as indicated at 3|, 32 and I9.

Referring again to Fig. 1, each amplifier unit is mounted upon brackets(not shown) extending from the chassis frame. These brackets as well asthe resistor and condenser panel [6 of each unit can not be seen on thedrawings as they are on the back side of the units. The grid lead ofeach amplifier unit extends from the high potential end of thetransformer secondary through the shielding cap 9. Therefore, it extendsfrom a point positioned at approximately the middle of the unit. Bystaggering the several amplifier units as illustrated, the point in anamplifier unit from which the grid lead extends is brought close to thegrid terminal of the succeeding amplifier whereby a very short grid leadmay be employed. This is of. great importance in amplifiers whichoperate at such high frequencies as those employed in television. Longergrid leads in such amplifiers cause instability and loss of gain.

It may be mentioned that in the television receiver from which theportion illustrated in Fig. 1 is taken, the first detector andsuperheterodyne oscillator (not shown) are mounted on the top of. thechassis frame I close to the first amplifier 3 whereby the intermediatefrequency output of the first detector may be supplied to the firstamplifier stage through a short lead. The detector and oscillator havenot been illustrated as do not form part of the present invention.

In Fig. 3 there is illustrated a slightly different embodiment of myinvention. In this figure my invention is shown applied to asuperheterodyne receiver designed for taking field strengthmeasurements. In order to simplify the drawings only the intermediatefrequency amplifier portion of the receiver has been shown. In thisreceiver. three intermediate frequency amplifier stages 36, 31 and 38,each of the type previously described, are mounted in staggered relationto each other on horizontal chassis frame 39. Each amplifier unit issupported from a bracket extending from the frame 39, the lower portionof the unit passing through an opening in the frame. Also each unit ismounted at an angle with respect to the horizontal frame and at an anglewith respect to the vertical panel 4| of the receiver whereby there is aconsiderable saving in space. The main feature of this arrangement isthat, as in the arrangement illustrated in Fig. 1, the grid leads of,the amplifier units are shortened sufficiently to avoid difiiculties inthe amplifier operation, these grid leads being indicated at 42, 43 and44.

By employing amplifier tubes in which the plate terminal, instead of thegrid terminal, is located at the top of each amplifier tube, theconnections of each amplifier unit may be changed by making theintermediate frequency transformer of each unit the one which precedesthe amplifier tube of the same unit. This arrangement, however, is notconsidered to be as satisfactory as the one illustrated for severalreasons, one reason being that either at the beginning or at the end ofthe intermediate frequency amplifier there will be one transformer whichis not contained in a complete amplifier unit.

From the foregoing description it will be apparent that variousmodifications may be made in my invention without departing from thespirit and scope thereof and I desire therefore that only suchlimitations shall be imposed thereon as are necessitated by the priorart and set forth in the appended claims.

I claim as my invention:

1. A high frequency amplifier comprising a plurality of amplifier units,each unit comprising an amplifier tube socket, an amplifier tubepositioned therein, and a transformer mounted in unitary relation withsaid socket to form an integral amplifier stage, each of said unitshaving means for shielding it from the other units, and a short signallead from said transformer extending from a point near the base of. saidtube, said tube being of the type having an electrode terminal on thetop thereof, said units including said shielding means being mounted instaggered relation with said point from which the short lead extendsadjacent to the said electrode terminal of the tube in a next adjacentamplifier unit.

2. A high frequency amplifier comprising a plurality of amplifier units,each unit comprising an amplifier tube and a transformer mountedunderneath said tube, each of said units having means for shielding itfrom the other units, and a short signal lead from said transformerextending from a point near the base of said tube, said tube being ofthe type having an electrode terminal on the top thereof, said unitsincluding said shielding means being mounted in staggered relation withsaid point from which the short lead extends adjacent to the saidelectrode terminal of the tube in a next adjacent amplifier unit.

3. A high frequency amplifier comprising a plurality of amplifier units,each unit comprising an amplifier tube and a transformer mountedunderneath said tube, each of said units having means for shielding itfrom the other units, a short output lead from said transformerextending from a point near the base of said tube, said tube being ofthe type having a grid terminal on the top thereof, and means formounting said units including said shielding means in staggered relationwith said point from which the output lead extends adjacent to the gridterminal of the next succeeding amplifier unit whereby said short leadmay be connected to said next adjacent grid terminal.

4. An amplifier comprising a plurality of am plifier units, each unitcomprising an amplifier tube and an intermediate frequency transformermounted underneath said tube to form a unitary structure, a shield forsaid transformer, a short signal lead from said transformer extendingfrom a point near the base of said tube, Said tube being of the typehaving an electrode terminal on the top thereof, said units includingsaid shields being mounted in staggered relation with said point fromwhich the short lead extends adjacent to the said electrode terminal ofthe tube in a next adjacent amplifier unit.

5. An amplifier comprising a plurality of amplifier stages, each stagecomprising a unitary structure including an amplifier tube socket for anamplifier tube of the type having a grid terminal at the top thereof anda transformer mounted underneath said socket and supported therefrom,said unitary structure including a shield for said transformer, saidtransformer having a primary connected to the output circuit of. saidtube and a secondary having output connections including a short gridlead, said amplifier stages being mounted in staggered relation with thegrid terminal of one amplifier unit being positioned close to the tubesocket of the next preceding amplifier unit.

6. A high frequency amplifier comprising a plurality of amplifierstages, each stage comprising an amplifier tube socket, an amplifiertube in said socket, said tube being of the type having a control gridconnected to a terminal on the top thereof, an intermediate frequencytransformer mounted on the side of said socket opposite said tube, saidtransformer having a primary and a secondary, a shield for saidtransformer, said transformer primary being connected to the platecircuit of said tube, a short grid lead extending from said secondarythrough said transformer shield, said amplifier stages including saidshields being mounted in staggered relation with respect to each otherwhereby the grid terminal of one tube is adjacent to the grid lead of anadjacent amplifier stage, the grid lead of each amplifier stage beingconnected to the grid terminal of the succeeding and next adjacentamplifier stage.

RALPH S. HOLMES.

